The invention relates to a plate-shaped filter holder for a sterilising container, including a peripheral outer pressure rim, a central pressure region, a mounting device for fixing the filter holder on the sterilising container, and including webs between the outer pressure rim and the central pressure region which leave open breakthroughs therebetween.
Such a filter holder for a sterilising container is known from DE 37 10 049 B1 for example. Extensive filter materials, for example paper filters or textile filters, can be pressed closely against breakthroughs in the sterilising container with the help of a plate-shaped filter holder, breakthroughs of this type being located in the lid of a sterilising container, in a side wall or in the base thereof for example. In order to fix the filter in position over a long period, it is necessary to press against the filter holder in a resilient manner and this is effected, in the case of the known arrangements, by means of a central mounting device which presses the filter holder against the filter bed by deforming it resiliently. In the case of the known filter holder, sealing is affected firstly by means of a seal around the outer pressure rim and secondly by means of a central seal in the central pressure region. In the known filter holders, the outer pressure rim is connected to the central pressure region by means of radial webs which leave open breakthroughs therebetween through which gas exchange can take place.
It has become apparent that stresses, which may lead to undesirable deformation of the filter holders, can occur in filter holders of this type. Such stresses occur, for example, when punching out the breakthroughs or during deep drawing processes by means of which the filter holder is formed into the desired shape. These undesirable deformations lead to the filter holder resting non-uniformly on the filter bed so that the sealing thereof cannot always be ensured. In order to prevent this, it is necessary to remove the distortions by subjecting the filter holders to an appropriate finishing process, for example by means of a heat treatment process.
The object of the invention is to construct a filter holder of the type described in the first part of claim 1 in such a manner that undesirable distortions are reliably prevented.
In accordance with the invention, this object is achieved in the case of a filter holder as described hereinabove in that the webs extend at least partially in a direction which comprises a component in the peripheral direction. surprisingly, it has been discovered that distortions will not occur if care is taken to ensure that the webs between the outer pressure rim and the central pressure region do not extend exactly in the radial direction, but rather that these webs extend a least partially in the peripheral direction or at least in a direction which has a component in the peripheral direction. By virtue of the webs extending in this manner, the material can flow continuously in the peripheral direction and should the production of stresses possibly occur, then stresses of this type will start to dissipate as soon as they occur. This is not possible in the case of webs which extend exclusively in the radial direction.
Geometrically, the webs may be very different in shape with the sole proviso however, that they have a component in the peripheral direction at least to a partial extent.
For example, provision may be made for the webs to extend between the central pressure region and the outer pressure rim in the form of curves.
It is also possible, for the webs to extend in straight lines between the central pressure region and the outer pressure rim whereby they then include an angle with the radial direction.
The webs may have a component acting in the same peripheral direction over their entire length, but in a modified embodiment it is also possible for the peripherally extending component of the web to alter its direction over the length of the web.
For example, the webs could extend in wave-like or zigzag form over their longitudinal extent.
In a particularly preferred embodiment, provision is made for the webs to compromise sections along their longitudinal extent which extend alternately radially and in the peripheral direction.
The webs may be in the form of independent components between the outer pressure rim and the central pressure region, but it is also possible for adjacent webs to be connected together by connecting webs. The stability of the filter holder will thereby be increased, but nevertheless undesirable distortions will be avoided because of the peripheral components in the path traced by the webs.
In a particularly preferred embodiment, provision is made for at least one middle web extending in the peripheral direction to be arranged between the central pressure region and the outer pressure rim, and for connecting webs having a radial component to be arranged between the middle web and the outer pressure rim, the inner pressure region or an adjacent middle web, said connecting webs being joined to opposite sides of the middle web and being mutually displaced in the peripheral direction. The connecting webs could extend, in particular, in the radial direction. One then obtains a construction in which radially extending webs do in fact extend between the central pressure region and the outer pressure rim, although they do not extend over the whole of the spacing between the outer pressure rim and the central pressure region, but rather, only over a partial region, namely up to the next middle web, and this middle web extends in the peripheral direction so that, in toto, the web connection between the outer pressure rim and the central pressure region extends alternately radially and in the peripheral direction. It is also ensured hereby that undesirable distortions are avoided.
In order to fix the filter material properly in place, it is expedient if a ring seal is held on the outer pressure rim and moreover, a resiliently deformable pressure seal may also be arranged on the central pressure region.
In a particularly preferred embodiment, this pressure seal is a lip seal having a resilient sealing lip which is adapted to be pressed onto the central pressure region. Such a sealing lip can be deformed to a relatively large extent, so that even with sealing materials of differing thickness, it is possible to ensure proper seating in the central region in every case, even when the spacing of the filter holder from the sterilising container is the same in every case. Tolerances in the spacing are accommodated by the great extent to which the sealing lip can be deformed.
It is expedient if the lip seal comprises an annular mounting body onto which the annular sealing lip is moulded.
In particular, provision may be made for the mounting body to comprise a recess into which the lip seal enters when it is pressed to the full extent against the central pressure region.
A particularly simple way of fixing this filter holder on the sterilising container ensues if, in accordance with a preferred embodiment, provision is made for the mounting device to comprise a housing having two locking bodies which are adapted to be resiliently displaced relative to one another in the peripheral direction and which engage behind a retaining member of the sterilising container, which projects through the filter holder, when in a non-displaced locking position but release it when in a displaced release position, for the housing to be adapted to be fixed to the filter holder in the central pressure region by a rotational movement in which respective projections and recesses on the filter holder and on the housing interlock, and for at least one releasable latch to be provided which prevents the housing from rotating relative to the filter holder when it is attached to the filter holder. Such a mounting device having two locking bodies which are adapted to be displaced relative to one another is known in the case of filter holders in accordance with the first part of claim 1 (DE 37 10 049 B1), but in this case, the housing is permanently connected to the filter holder, for example by means of rivets, screws, etc. In the case of the construction being described however, the housing is connected to the filter holder by a rotational movement similar to that of a bayonet connection, and it is prevented from being unintentionally released by virtue of the releasable latch. Consequently, it is possible to fix the housing on to the filter holder by means of the two locking bodies without using a tool and without using additional parts.
It is particularly advantageous hereby, if the latch is formed by one of the two locking bodies which prevents the housing from rotating when in its locking position and releases the housing when in its release position. In this embodiment it is not necessary to provide a separate latch, but rather, the locking body in the housing that is displaceable against spring force also takes on the task of a latch which prevents the housing from being unintentionally rotated and released.
Furthermore, is particularly advantageous if the other locking body prevents the housing from rotating when in its release position and releases it when in its locking position. It is thereby ensured that during the displacement of the locking body into its release position, i.e. the position in which the filter holder releases the retaining member of the sterilising container and can be removed from the sterilising container, the housing cannot be unintentionally rotated and removed from the filter holder. In order to rotate the housing, one of the two locking bodies must be displaced into the release position, whereas the other locking body must remain in the locking position. Consequently, rotation of the housing is not possible when both of the locking bodies are in the locking position, nor, when the two locking bodies are in the release position. Only these two positions will occur in normal operation of the filter holder since the two locking bodies are displaced from the locking position into the release position by diametrical pressure. On the other hand, if it is intended to rotate the housing relative to the filter holder so as to remove the housing, one must take deliberate care that only one of the two locking bodies is displaced.
Hereby, in a particularly preferred embodiment, provision is made for cam tracks and projections, which are guided therein, on the central pressure region and on the locking bodies respectively to co-operate and thereby allow the housing to rotate relative to the filter holder only in said certain positions of the locking bodies.
Thus, for example, provision may be made for one cam track for the locking body which secures the housing in its locking position to comprise a radially inwardly directed section, and, adjoined to the inner end of this section and adjacent thereto, an outwardly extending section. By having such a section, it is ensured that it is only possible to rotate the housing relative to the filter holder when the corresponding locking body has been moved into the release position.
Furthermore, it is expedient if one cam track for the locking body which secures the housing in its release position comprises a radially inwardly directed section, and a peripherally extending section adjoining the outer end of said first-mentioned section. Thus, this locking body only enables the housing to be rotated when it is itself in the locking position, whereas the housing is prevented from rotating relative to the filter holder in every other position.
In particular, provision may be made for the radially inwardly directed sections of the cam tracks and the projections engaging in the cam tracks to be arranged such that they are mirror symmetrical relative to the rotational axis of the housing. It is thereby possible to arrange the cam tracks and the projections such that the housing can be seated on the filter holder in two positions displaced by 180xc2x0 whereby each of the two locking bodies can take on the role of that locking body, which prevents the housing from rotating in the release position or in the locking position, in dependence on the orientation at which the housing has been seated, i.e. one can utilise a completely symmetrical construction for the locking bodies and one does not have to be careful when seating the housing as to which projection engages in which cam track.
To this end, it is also expedient if the end points of the sections adjoining the radially inwardly directed sections are arranged such that they are mirror symmetrical relative to the rotational axis of the housing.